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​​Our Transmiss​ion CorridorsTransmission1.jpg

Hydro One regularly patrols our transmission rights-of-way to identify trees and other vegetation that could interfere with the safe operation of power lines. Our forestry technicians specifically seek to identify incompatible vegetation and promote the growth of compatible vegetation.

Incompatible Vegetation Vs. Compatible Vegetation

Incompatible Vegetation

Incompatible vegetation includes any plant or tree species that, at maturity, could interfere with the safe operation of power and grow within the clearance area required ​​by provincial​​​ and industry standards including the Occupational Health and Safety Act (OHSA), Canadian Sta​​ndard Association (CSA) and standards set by the Company. Hydro One removes incompatible vegetation   from our rights-of-way through routine vegetation
maintenance programs which
we target to complete on a six to eight year cycle
depending on the location within the province and local conditions.

Compatible Vegetation Picture1.jpg

Hydro One's vegetation maintenance programs are designed to promote the regeneration and re-establishment of compatible vegetation among the ground cover. By selectively removing trees we are encouraging a more robust and species diverse ground cover that won't threaten the overhead lines and will reduce future vegetation maintenance activities. Vegetation deemed as compatible by Hydro One's forestry technicians, will be left untouched.

Maintaining Minimum Clearances

When conducting routine vegetation management, Hydro One also considers the required minimum clearance between power lines and vegetation along each right-of-way.

Minimum clearances are regulated by OHSA, CSA and Hydro One standards, and are determined by a number of factors. These include the point of maximum sag of a power line and the expected plant growth until the next maintenance period.

Maximum sag is the lowest possible distance a power line can drop, during peak load and very warm temperatures.

On a hot summer day, a power line will sag more than on a cooler winter day, making the centre of the line much closer to the ground and vegetation. The line will also sag more as the electricity load increases. In the summer, a transmission line can sag many metres more than the same line carrying the same amount of electricity in winter, due to increased load. 


Maximum sag is measured at maximum load on a very hot day.
Even at maximum sag, a 230 kV line must be 4.5 metres from the nearest vegetation.



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